A. Field of the Invention
The present invention relates to an automatic transmission apparatus including a torque converter which has a multi-speed configuration.
B. Description of the Background Art
The assignee of the present application has previously proposed various kinds of structures for automatic transmission apparatuses, in which a four-element torque converter is used with automatic transmissions. In the four element torque converter, the four elements include a turbine, a first stator, a second stator and an impeller. The turbine and at least one of the two stators are coupled to portions of the transmission to produce an output by combining torque transmitted from them. These automatic transmission apparatuses can be classified into the following three types.
According to a first type of an automatic transmission apparatus, which is disclosed in Japanese Patent No. 1,965,369 (Japanese Patent Application Number 60-25906), and U.S. Pat. No. 5,122,104, forward rotation power of a turbine and reverse rotation power of a stator are output from a torque converter when a 1st (forward 1st) speed and a reverse are selected. When a 2nd speed is selected, the stator is fixed and the rotation power is transmitted only from the turbine. When a 3rd speed is selected, the turbine is integrated with the stator. U.S. Pat. No. 5,122,104 is herein incorporated by reference.
A second type of an automatic transmission apparatus, is disclosed in Japanese Patent Nos. 1,871,294, 1,896,991, 1,896,992 and 1,963,199, which correspond to Japanese Patent Application Numbers 61-101504, 61-101505, 62-101506 and 61-101446, respectively. Japanese Patent Application Numbers 61-101504, 61-101505, 62-101506 and 61-101446 were combined and subsequently issued as U.S. Pat. Nos. 4,869,128 and 4,942,779. U.S. Pat. Nos. 4,869,128 and 4,942,779 are both incorporated herein by reference. The second type of an automatic transmission apparatus disclosed in U.S. Pat. Nos. 4,869,128 and 4,942,779. U.S. Pat. Nos. 4,869,128 and 4,942,779 differs from that disclosed in U.S. Pat. No. 5,122,104 in that the reverse driving is performed by fixing the turbine and supplying the rotation power from the stator.
A third type of transmission and torque converter is disclosed in Japanese Patent Nos. 1,785,235 (Application No. 59-195410) and 1,962,867 (Application No. 60-7233). In the third type, the forward rotation power of the turbine and the reverse rotation power of the stator are transmitted at all speed settings of the transmission. The disclosures of Japanese Patent Nos. 1,785,235 and 1,962,867 are herein incorporated by reference.
According to these types of automatic transmission apparatuses, the rotation power can be supplied also from one of the stators in contrast to a general transmission apparatus utilizing only an output of the turbine. Therefore, in the above described transmissions, the power output can be relatively large.
The assignee of the present application has also proposed another novel structure in Japanese Patent Application No. 7-234386 (1995). In this structure, a turbine of a torque converter is coupled to a first output shaft via a planetary gear train, and a stator is coupled to a second output shaft via a one-way clutch. Further, another one-way clutch is arranged between a sun gear of the planetary gear train and the second output shaft, and a reverse rotation power of the sun gear is transmitted to the second output shaft via this one-way clutch.
According to this structure, the transmission can output a further larger power compared with the first and third types, and the number of speeds can be increased.
However, the above structure disclosed in Japanese Patent Application No. 7-234386 suffers from such a problem that an engine brake cannot function during reverse driving in 1st and 3rd speeds when the sun gear reversely rotates faster than the second output shaft, because the one-way clutch is arranged between the sun gear of the planetary gear train and the second output shaft. Further, it suffers from complicated structures, increase in weight and size and increase in manufacturing cost, because two one-way clutches are arranged in the torque converter.